Direct nitration of o-sec-butylphenol with nitric acid in a lower carboxylic acid

ABSTRACT

O-sec-butylphenol is nitrated with nitric acid in a lower carboxylic acid solvent and optionally in the presence of an oxidation inhibitor selected from a secondary or tertiary alcohol, a secondary alkyl nitrate, an aldehyde or a ketone. Use of such solvents and inhibitors decreases the quantity of oxidation products formed, especially secondary butyl-quinone formation.

United States Patent [191 Anderson et al.

[ Jan. 14, 1975 DIRECT NITRATION OF O-SEC-BUTYLPHENOL WITH NITRIC ACID IN A LOWER CARBOXYLIC ACID [75] Inventors: Gene A. Anderson; Robert E.

Bailey; Wilson F. Gum, Jr., all of Midland, Mich.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: Nov. 20, 1970 [21] Appl. No.: 91,535

Coffield 260/622 R 3,694,513 9/1972 Tobey et al. 260/622 R OTHER PUBLICATIONS Mankovits, Berichte, vol. 41, p. 2335, (1908). lputieff, J.A.C.S.," pp. 2495-2497, vol. 60, (1938). Fileti, Gazz. Chim., ltal. Vol. 16, pp. ll7l26, (1886).

Primary ExaminerBernard Helfin Assistant ExaminerW. B. Lone Attorney, Agent, or Firm-Sidney J. Walker [57] ABSTRACT O-sec-butylphenol is nitrated with nitric acid in a lower carboxylic acid solvent and optionally, in the presence of an oxidation inhibitor selected from a secondary or tertiary alcohol, a secondary alkyl nitrate, an aldehyde or a ketone. Use of such solvents and inhibitors decreases the quantity of oxidation products formed, especially secondary butyl-quinone formation.

6 Claims, No Drawings DIRECT NITRATION OF O-SEC-BUTYLPHENOL WITH NITRIC ACID IN A LOWER CARBOXYLIC ACID BACKGROUND OF THE INVENTION The direct nitration of o-sec-butylphenol has been avoided because of the competitive formation of oxidation by-products. Such oxidation has been traditionally circumvented by first sulfonating the phenol and then reacting the sulfonate with a nitrating agent to replace the sulfonic acid group with the nitro group. A number of techniques for such treatment are well known and are exemplified by Urbanski in Chemistry and Technology of Explosives, Vol. 1, Pergamon Press, New York, 1964.

The direct nitration of cresols with nitric acid in an acetic acid solvent is shown by Gordon et a]. in US. Pat. No. 3,517,074. These nitrations were conducted at 25 to 55C. to give dinitrocresol. The direct nitration of o-sec-butylphenol, however, is different than the direct nitration of cresols because of the large amounts of secondary butylquinone formed in the conventional direct nitration of o-sec-butylphenol.

Dietzler in US. Pat. No. 2,802,883 teaches the direct nitration of t-alkylphenols in carbon tetrachloride or perchloroethylene. These reactions were conducted at temperatures of about to about 75C. by adding the alkylphenol solution dropwise into nitric acid.

SUMMARY OF THE INVENTION It has now been discovered according to the present invention that in the direct nitration of o-secbutylphenol (OSBP) where OSBP is contacted with nitric acid in the liquid phase in the presence of a solvent to give a nitration product, the formation of secondary butylquinones is substantially reduced by the use of a lower carboxylic acid as solvent. Moreover, it has further been discovered that the use of the lower carboxylic acid solvent in combination with an oxidation inhibitor selected from the group consisting of a secondary or tertiary alcohol, a secondary alkyl nitrate, an aldehyde, a ketone or mixture thereof, gives a greater reduction in the amount of oxidation by-products. These techniques of manipulating the reaction provide a convenient and effective method of nitrating OSBP without the loss of substantial quantities of reactants to undesirable by-products.

The central aspect of the present invention is the use of a lower carboxylic acid as the solvent in the direct nitration of OSBP. By the term lower carboxylic acid is meant acetic acid, propionic acid or mixture thereof. Of these two acids, the use of acetic acid as the solvent is preferred because of its availability and effectiveness.

The carboxylic acid solvent may be used in any amount which significantly reduces the secondary butylquinone formation. This amount may vary widely, but generally is more than about 2 moles of solvent for each mole of OSBP nitrated. In other respects, this particular solvent is employed according to known solvent techniques, such as use with cosolvents, recovery of product and solvent recycle.

An ancillary but integral aspect of the invention is the use of an oxidation inhibitor in addition to the lower carboxylic acid solvent. These inhibitors, generically described above, must be liquid at reaction temperature and at least partially soluble in the reaction medium. Inhibitors having carbons or less usually meet these criteria. Representative examples of suitable inhibitors include: secondary alcohols, such as 2-,

propanol, 2-butanol, 2-pentanol, 3-hexanol, cyclohexanol, 3-decanol, 4-dodecanol and 2-octanol; tertiary alcohols, such as t.-butyl alcohol, t.-amyl alcohol and 3- ethyl-3-hexanol; secondary alkyl nitrates such as isopropyl nitrate, 2-butyl nitrate, 3-pentyl nitrate, 2- dodecyl nitrate and 2-heptyl nitrate; aldehydes such as acetaldehyde, pentanal and undecanal; ketones such as acetone, 2-butanone, 3-pentanone, 2,2-dimethyl-3- butanone, 4-nonanone and S-undecanone. Inhibitors of not more than eight carbon atoms are preferred, with 2-propanol, 2-butanol and acetone being especially preferred, and 2-propanol being of particular interest because of its special effectiveness in reducing oxidation products.

The concentration of the inhibitor in the reaction may vary widely as different inhibitors, lower carboxylic acid solvents and conditions are employed. Any small but'effective amount which reduces the amount of by-products formed in the reaction over and above the benefit derived from the carboxylic acid is suitably employed. Preferably concentrations of about 5 to about 100 mole percent of the inhibitor, based on the OSBP, are used, with concentrations of 10 to 50 mole percent being especially preferred. Above concentrations of 100 mole percent, the nitric acid is inefficiently employed because of the side reaction with the inhibitor and below concentrations of about 5 percent, the reduction in the by-products formed is substantially diminished.

The concentration of the nitric acid may suitably range from about 20 weight percent to fuming nitric acid, with 60 percent to 90 percent nitric acid being preferred. Usually a molar excess of nitric acid based on the OSBP is employed to insure the desired degree of nitration while minimizing the possibility of oxidation by-products. For example, in the preferred dinitration, about 2.2 to about 4 moles of nitric acid are employed per mole of OSBP.

The temperature of the reaction may vary widely so long as the liquid phase is'maintained. Preferred temperatures are about 10 to about 85C. or more, with temperatures of 40 to C. being especially preferred. Since the reaction is exothermic, cooling is usually required. At these temperatures, the reaction time may vary widely depending upon the proportions of reactants, solvent and inhibitor. Under the conditions of the specific embodiments, the reaction is usually complete in less than an hour and, in most instances, less than 30 minutes.

The process of the present invention is easily conducted in a batch process, or it is readily adapted to a continuous operation. In a continuous operation, a mixture of the OSBP, solvent and inhibitor is continuously fed into a suitable reactor, such as an elongated tube, and simultaneously concentrated aqueous nitric acid is fed concurrently into the reactor from a separate source. The reactants are maintained at reaction temperature for the desired time with stirring and at the termination of the reaction, the nitrate product is isolated from the organic layer by conventional means.

SPECIFIC EMBODIMENTS Examples 1-9 and Comparative Examples A-B Dinitration of OSBP in Acetic Acid In parallel experiments, a well-stirred reactor was charged with OSBP, 70% HNO acetic acid and in some cases an inhibitor in the molar proportions noted in Table I. The reactor was maintained at 55C. and the reaction was carried out until all of the OSBP had reacted to give about a 90 percent yield of product. The desirability of the system was monitored by measuring the amount of oxidation by-product, o-secbutylquinone (SBQ), found in the dinitro-o-secbutylphenol (DNOSBP) reaction product by vapor phase chromatography (VPC). The results, showing the benefit of the application of the invention over the direct nitration of OSBP alone and in a solvent of CCI are given in Table I.

TABLE I Effect of Solvent and Inhibitors on the Direct Dinitration of OSBP Examples 10-ll and Comparative Examples A-B Direct Dinitration of OSBP in Propionic Acid In the same manner as shown in Example 1, OSBP was nitrated with nitric acid in propionic acid with and without additional inhibitor. The DNOSBP product isolated contained the SBQ concentrations shown in Table II.

TABLE II Direct Dinitration of OSBP in Propionic Acid SBQ, Reactant Conc., mole/mole VPC Example Inhibitor OSBP/HNOJPropAcid/Inhib.

Comp. A None l/3.5//O 5.7 Comp. B None l/3.5/3.0 of CCIJO 6.6 None l/3.5/3.l/0 4.0

' ll Z-Propanol 1/3.5/3.l/0.2 2.9

Example 12 Continuous Dinitration of OSBP To a well-stirred continuous-flow reactor constructed from a cylinder having an inlet for reactants and an overflow outlet for products leading to a stirred round bottom flask used as a holding tank, OSBP, I

HNO acetic acid and 2-propanol were fed at a mole ratio of 1/3.0/4.0/0.2. The rate of flow was adjusted to give an average residence time in the reactor of 20 minutes and residence time of 32 minutes in the holding tank. The temperature of both the reactor and holding tank was 55C. The DNOSBP was separated from the holding tank effluent by allowing the product to form two layers and separating the layers to isolate DNOSBP in the bottom layer. The product collected during the second hour of operation, about 400 g., had a 0.9 percent concentration of SBQ. The conversion was 100 percent, and the yield was percent.

In the same manner as shown by the examples above, other inhibitors, such as 2-butanol, 2-hexanol, 4- tridecanol, t-amyl alcohol, isopropyl nitrate, 2-decyl nitrate, acetaldehyde, dodecanal, methyl isobutyl ketone, methyl ethyl ketone and 3-octanone, may beused in the nitration of OSBP with nitric acid in a solvent of acetic acid, propionic acid or mixture thereof to reduce the formation of SBQ.

We claim:

1. A process for the liquid phase direct nitration of o-sec-butylphenol (OSBP) comprising contacting OSBP with nitric acid having a concentration of from about 20 weight percent to fuming nitric acid in the presence of a lower carboxylic acid solvent selected from the group consisting of acetic acid and propionic acid in an amount to reducesecondary butylquinone formation and from 5 to mole percent based on the OSBP of a liquid oxidation inhibitor, which is at least partially soluble in the reaction medium, selected from the group consisting of 2-propanol, 2-butanol, 2- pentanol, t.-butyl alcohol, isopropyl nitrate, acetaldehyde, acetone and 2-butanone at a temperature of from about 10 to about 85C.

2. The process of claim 1 wherein the oxidation inhibitor contains not more than eight carbons.

3. The process of claim 2 wherein the oxidation inhibitor is 2-propanol.

4. The process of claim 1 wherein the concentration of the oxidation inhibitor is 10 to 50 mole percen based on the OSBP.

5. The process of claim 1 wherein the temperature is about 40 to about 75C.

6. The process of claim 1 wherein the solvent is acetic acid. 

2. The process of claim 1 wherein the oxidation inhibitor contains not more than eight carbons.
 3. The process of claim 2 wherein the oxidation inhibitor is 2-propanol.
 4. The process of claim 1 wherein the concentration of the oxidation inhibitor is 10 to 50 mole percent based on the OSBP.
 5. The process of claim 1 wherein the temperature is about 40* to about 75*C.
 6. The process of claim 1 wherein the solvent is acetic acid. 